Degradation of signal-to-noise ratio (“SNR”) occurs to a signal carried along a transmission medium (e.g. coax, unshielded conductor, wave guide, open air or even optical fiber). SNR degradation is one factor which may limit bandwidth over a transmission medium. In order to improve the SNR of signals being transmitted over long distances, and accordingly to augment the transmission distance and/or data rate, signal repeaters may be placed at intervals along the transmitting path. Repeaters are well known and may be used for optical, microwave and radio frequency (RF) communication systems. Repeaters have been used as part of cellular transmission systems to extend the range of coverage between a cellular base station and a cellular handset.
However, the use of a repeater for one or more channels at one or more frequencies within a shared frequency range of the spectrum (e.g. 800 MHz to 830 Mhz) may produce interference. Turning now to FIG. 1A, there is shown a spectral diagram exemplifying the channel frequencies a first cellular operator may be using within the frequency range of 800 to 830 MHz. Turning now to FIG. 1B, there is shown a spectral diagram exemplifying the channel frequencies a second cellular operator in the same geographic location as the first may be using within the same frequency range, 800 to 830 MHz. As can be seen from the FIGS. 1A and 1B, each operator's channel frequencies may be distinct from the other. However, two or more channel frequencies of one operator may either be between two or more channel frequencies of the other operator or may be on either side one or more of the other operator's channel frequencies.
In order for an operator to use a repeater in the situation described above and exemplified in FIGS. 1A and 1B, the operator would either need a separate response for each channel, or the operator may use a broader band repeater to cover a frequency range within which several of the operator's channels reside. However, if a broader band repeater is used, the repeater may inadvertently retransmit one or more channels belonging to both operators. The retransmission of another operator's communication channel(s) has both legal and business implications which a cellular operator may prefer to avoid.
Analog channelized repeaters exist in the prior art. Channelized repeaters of the prior art use analog filters to exclude or filter out all signals or communication channels not belonging to the operator whose channels are to be repeated. For example, if the repeater's band of operation is 800 to 830 MHz, and the operator using the repeater has communication channels at 805 MHz, 807 MHz, and 809 MHz, the repeater may be equipped with analog filters which only allow or pass signals at the frequencies of the operator's channels. The analog channelized repeater thus retransmits only signals at the frequencies of the operator's communication channels.
Analog channelized repeaters of the prior art have numerous drawbacks which the present invention aims to address.